The aim of this research proposal is to study the neurobiological substrates of short-term memory by comparing two groups of neuropsychological patients. Both patients with anterior (prefrontal cortex) lesions and conduction aphasics with posterior (temporo-parietal cortex) lesions exhibit short-term memory deficits. It is hypothesized that the two groups' deficits arise from impairment in different components of short-term memory. To assess this hypothesis, the two patient groups and elderly controls will be administered a series of tasks requiring short-term memory. These tasks will vary along several dimensions, such as the domain of the task (verbal versus spatial). Findings from this research will illuminate understanding of normal short-term memory processes as well as identify the brain regions mediating those processes. In addition, this research has implications for treatment (e.g., cognitive rehabilitation) of patients with similar brain injuries and cognitive deficits.